Together, they have a population of fewer than 2,000, but the tiny East Texas hamlets of Reklaw, Alto and Gallatin have an outsized mission: To halt the southern portion of TransCanada's Keystone XL pipeline, a conduit designed to ferry some 830,000 barrels of Canadian tar sands a day from an Oklahoma hub to Gulf Coast refineries.

To that end, the towns -- a couple of hours east of Dallas -- have joined the Sierra Club in a suit against the U.S. Army Corps of Engineers in an Oklahoma federal court, claiming the corps is skirting a rigorous environmental impact analysis on more than 1,000 water crossings by "piecemealing" approval in half-acre segments.

Congress tried to force President Barack Obama's hand in 2011, when it passed a bill that required him to make a decision on the 1,300 mile Keystone XL within two months. In its assessment, the EPA warned against the type of permit TransCanada sought, which, in effect, would have placed no limit on the amount of collective damage the pipeline could cause to the water bodies it crossed. In January, the U.S. State Department said it didn't have enough time or information to determine the pipeline's environmental impact -- particularly on the massive Ogallala Aquifer in Nebraska's Sand Hills -- and recommended that Obama deny the permit. It said it would revisit its decision in 2013. Denied a permit for the entirety of the Keystone XL, TransCanada announced it would split the pipeline project in February, seeking a presidential permit for the northern section and immediate approval for the nearly 500-mile southern section, now renamed but tracing essentially the same path.

Obama voiced his support, asking regulators to fast-track the permitting process. In late June, TransCanada received notification from Corps of Engineers offices in Galveston and Tulsa that the southern portion of the pipeline could be permitted as a project with minimal impacts on water crossings -- even though the EPA had cautioned that more than half of the crossings exceeded the damage limit. "We found out the EPA letter was withdrawn because it isn't called the Keystone XL," says Rita Beving, the towns' consultant. "It's called the TransCanada southern segment. It's the same route, the same pipeline, just the semantics of calling it another name makes the letter not viable."

The final approval needed from the Fort Worth office of the Corps of Engineers could come at any time, allowing construction on the pipeline, the plaintiffs say, to begin within 45 days.

The towns of Reklaw, Alto and Gallatin are asking the federal court to vacate the corps' permits, claiming irreparable injury if the project proceeds. More than anything, they fear the specter of a pipeline spill and contamination to their main water source: The Carrizo-Wilcox Aquifer, which supplies some 60 counties and 10 to 12 million people with water. But it isn't just the Carrizo that could be in jeopardy, Beving says. The pipeline passes near Lake Columbia, Marvin Nichols Reservoir` and George Parkhouse Reservoir -- all prospects for Dallas as it seeks to firm up water rights for a swelling population.

The pipeline won't just be carrying ordinary oil. Sweet crude, for example, is moved through pipelines at around 150 pounds per square inch, smooth as molasses. The Keystone pipeline will carry tar sands, also known as DilBit -- a highly corrosive and benzene-laced mixture of sand, clay water and bitumen mined from arboreal forests in Alberta and pumped at some 1,400 pounds per square inch. The pressure is so great a leak in another Keystone pipeline once shot tar sands six stories high.

In 2010, an Enbridge pipeline spilled a million or more barrels of tar sands into Michigan's Kalamazoo River, fouling some 35 miles and spiking it with astronomical levels of benzene, a known carcinogen. It was the largest onshore spill in history, and investigators concluded Tuesday that the company knew about the pipeline defect for years and failed to address it.

"If these folks have water contamination, what are (the towns of Reklaw, Alto and Gallatin) going to do?" Beving says. "Emergency response? They have volunteer firefighters. They would have to get help from fire departments in Tyler or Longview with HAZMAT backgrounds."

For some of these towns, that's more than an hour away. The risk are too high, they believe, for the aquifer and for generations to come. Imagine if Dallas used its considerable heft to weigh in, if for no other reason than to secure our interests in a state where water will one day be more precious than oil?